Malignant glioma growth is characterized by extensive tumor infiltration associated with breakdown of the blood brain barrier (BBB). To determine the effect of reduced BBB breakdown on glioma infiltration we have developed an orthotopic xenograft mouse brain tumor model in which gliomas are implanted into immunodeficient Src knockout mice (Src KO). The Src KO mouse has been previously shown to mediate a reduction in glioma-induced BBB breakdown that was associated with reduced glioma infiltration, but independent of direct effects on glioma growth in general. In this model the focus is on effects of the host compartment (i.e. Src defects in the vascular endothelium) rather than on the more common analysis of tumor cells themselves (i.e. tumor compartment). The proposed studies are responsive to the PAS ("Understanding mechanisms of brain tumor dispersal") by outlining a novel proteomics strategy to identify and quantitate Src-mediated changes in expression and phosphorylation in response to glioma-mediated BBB breakdown in Src KO vs. wild type (WT) mouse brains. In contrast to RNA analyses, proteomics enables the detection of changes in protein expression without introducing a bias from variable translational efficiency/stability of different mRNAs. In Aim 1 endothelial cells will be isolated from tumor-bearing Src KO and WT mouse brains to identify Src-regulated proteins. For each candidate Src-mediated target molecule identified in Aim 1, we will validate the function of a candidate hit in a BBB reconstitution assay in Aim 2. The value of these studies is the identification of protein expression changes in the blood brain barrier (BBB) associated with glioma invasion using a knockout model with a well-defined phenotype exhibiting: 1) reduced VEGF-induced breakdown of the BBB;2) reduced glioma-induced breakdown of the BBB;3) reduced glioma invasion;and 4) reduced glioma-induced perivascular fibrin(-ogen) accumulation. This xenograft/proteomics approach is a novel strategy with much wider implications for tumor-host interactions, since it enables the identification of host-derived (i.e. mouse) vs. tumor-derived (i.e. human) proteins in the tumor-induced remodeling of the tumor microenvironment. PUBLIC HEALTH RELEVANCE: These studies address the PAS-06-201 (Understanding mechanisms of brain tumor dispersal) by analyzing changes in protein expression in blood vessels that mediate the breakdown of the blood brain barrier. The identification of these proteins will lead to a better understanding of the mechanisms regulating brain tumor dispersal and the future design of innovative therapies that target the host rather than tumor cells themselves.